Art of cracking hydrocarbon oils



July 23, 1929. E. w. lsoM ART UF CRACKING HYDROCARBON OILS Filed May 21, 192'? 9m. bm.

INVENTR Edu/am( /i/ [Salm vantage'ous in connection with`the simulta- Patented July. 23, 1929.

UNITED STATES P ,'OFFICE.

EDWARD W. ISOM, OF SGARSDALE, I NEW YORK, ASSIGNOR T0 lSINCIL'AIR BEFINING COMPANY, 0F NEW YORK, N. Y., A CORPORATION 0F MAINE.

ART OF CRAGKING HYDROCARBON OILS. i

Application led May 21,

This invention relates to improvements in the cracking of heavier hydrocarbon oils, such as'gas oil or kerosene, in order to produce therefrom lighter hydrocarbon oils, such as gasoline or pressure distillate. The invention relates particularly tov improvements in cracking operations carried out in externally heated, single pass, tubular oil cracking stills. In referring to single pass cracking operations, reference lis made to cracking operations in which the oil] supplied is circulated but once through the-oil heating tubes of the still. 'Ihe invention includes operations in which vaporized fractions are i'efiuxed and recirculated through the oil heating tubes, but it is to be distinguished from operations in which the fresh oil itself or any unvaporized portion thereof is recirculated through the heating tubes. This application is in part a continuation of my prior application filed August 28, 1922, Serial No.` 584,711.

The invention provides an 'improved method of cracking different grades of hydrocarbon oils in which each grade of oil is treated under conditions most advantageous for the lcracking of that particular grade of oil and in which the several operations are combined in such a manner that a greater yield, better quality of product and more f eflicient operation may be obtained than litV v is possible to secure by the separate treatment of the individual gradesof oil or a similar treatment of the oil mixture. The process of the invention is particularly` adneous treatment of relatively heavy hydrocarbon oils, such as gas oil or fuel oil, and of lighter and more refractory oils, such as kerosene or rerun pressure distillate bottoms. v In the cracking of the more refractory hydrocarbon oils, for example, kerosene or very light gas oils, it is advantageous to use a higher temperature to produce the desired cracking reaction, say to produce gasoline, than is commonly used in the treatment of heavier oils, and treatment of the heavier grades of hydrocarbon oils at thev temperatures requiredV to crack the more refractory constituents of lighter grades Within comnercially practicable periods oftime results 1n the formation of excessive quantities of xedggases and carbon or coke.

n In the" combined treatment ofZ different grades of oil according to the present inven- 1927. Serial No. 193,191.

tion, a streamof the more refractory lighter oil 1s passed once through a heating conduit andheatedV therein to a crackingtemperature and the hot products from the heating conduit are 'discharged directly into a body of oil to which less refractory heavier oil 1s supplied, this body of oil is maintained at a cracking temperaturefvapors are taken off from this body of oil and subjected successlvely to two refluxing operations, inthe first the vapors are cooled and partly condensed by indirect heat exchange with :freshv less refractory heavier oil supplied directly to the body of oil, in the second the vapors are further cooled'and condensed by indirect heat exchange with fresh more refractory lighter oil, and reflux condensate from both refluxing operations together With fresh more refractory lighter oil preheated in the second reluxing operation is supplied to the' heating conduit. The body. of oil may be heated externally as vvellr asinternally by the hot products discharged into it from the heating conduit, but it is advantageously exernally unheated and heated internally on y.

At the higher temperatures employed in; cracking the more refractory oils it is essential for safety and eiciency of operation to protect the heating tubes against overheating and the formation of carbon deposits therein and at the-same time to maintain a high average temperature differential betweenthe heating gases and the heat transferring surfaces. In the operation of the present inventionthe deposition of carbon in the heating tubes is avoided by circulating therethrough only the more refractory oils which do not cause excessive carbon formation at the tempertures 4employed and avoiding the recirculation of unvaporized oil which has been once subjected to cracking conditionsand which accordingly contains,'

temper the latter priorI to their contact with the oil containing tubes. By recirculating a portion of the heating gases the volume and accordingly the-velocity of the heating gases contacting with the heating tubes is increased. The increased velocity promotes an increase in the rate, and a more uniform distribution of the h eat absorption through out the bank ofheating tubes. Thus, the extremely high Vtemperatures necessary for most efficient combustion of the fuel used may be permitted without subjecting the oil containing tubes to contact with heating gases at excessive temperatures while at the same time a large portion of the heat contained in the products of combustion is eiiiciently transmitted to the oil being treated.

The higher temperature used to 'crack the lighter and more refractory hydrocarbon oil tends to promote the formation of fixed gases and unstable, unsaturated compounds,

troduced into a bod the presence of which is objectionable in the finished product. In the operation of the present invention, however, in which the lighter oils are separatelyy heated to their cracking temperature and subsequently inof heavier oil maintained at the` crac 'ng temperature, the unsaturated"constituents formed in the first operation apparently tendto react with constituents of the body of hot heavier oil to form more saturated compounds. An increased yield of constituents suitable. as components of the desired gasoline or pressure distillate is obtained and the formation of fixed gases and unstable, unsaturated compounds reduced.

The additional fresh oil supplied to the body of heavy oil is advantageously preheated to subst'antiall the temperature of the liquid body be ore its introduction thereinto and the amount of heat required to be supplied externally to the liquid body .irr order to maintain it at the cracking tem'- perature thereby further materially reduced.

In some cases. the application of external heat to the reservoir -may be dispensed with entirely, thereby avoiding any danger incident to the 'formation of heat insulating carbon deposits on the heated surfaces of the reservoir. The additional fresh'heavy oil introduced to the reservoir may advantageously be passed in countercurrent flow and indirect heat exchanging relation with the vapors generated inthe cracking operation beforey the latter are permitted to cool appreciably. The fresh oil may thus be preheated to a temperature approachingl the temperature ofthe liquid body to which it is introduced and the vapors refluxed by Ithe cooling effect of the fresh oil.V The vapors remaining uncoudensed' may advantageously be subjected to a further refluxing operationoin indirect heat Aexchanging relation with the fresh oil and this further re- 4fluxing operation controlled by regulating -the supply of the fresh lighter oil thereto so that the desired gavsoline product or pressure distillate may be directly produced without subsequent redistillation. The r`eflux condensates from both refluxing operations together with the fresh lighter oilv supplied to the latter reiuxing operation may be returned directly'to the single pass heating conduit and additional lighter oil may be independently supplied therewith as described. It will be noted, however, that neither the heavier oil itself nor any of its -unvaporized constituents are permitted to pass through the heating conduit with the more refractory constituents.

into a shell still or reservoir from which the vapors of the cracked oil are taken olf. Thel single-pass cracking still or heater comprises a furnace 1 in which a battery of heating tubes 2 are arranged. Oil is forced through -the heating tubes by means of a pump 3,.

entering the heating tubes through connecy tion 4 and, after passing once therethrough, being discharged through connection 5.

The heating furnace 1 is provided with a firebox 6 and a stack flue 7 heating gases being circulated from the irebox through the heating furnace over the oil-containing heating tubes therein to the stack flue.- The rebox 6 is provided with means for burning the fuel employed to supply the heat used in the -cracking operation. A burner for gaseous or liquid fuel is shown at 8. Before the hot products of combustion in the' irebox -6 come 4in contact with the oil heating tubes 2 in the furnace 1, they are admixed with a partv of the 'heating gases which have passed over the-oil heating tubes and which are returned through connection 9. The connection 9 is provided with an inlet 10 adjacent the exit to the .stack flue from the Afurnace and with van outlet 11 through which the heating gases withdrawn from near the -outlet of the furnace 'are returned and ad-v mixed with the hot' products of combustion.

The return connection 9 includes a blower 12 which maybevoperated by a steam jet 13 or other suitable means for maintaining circulation of the returnedheating gases;v

v The oil forced throughthe heating tubes 2 includes fresh oil and constituents reluxed from vapors of the cracked oil discharged from the single pass crackinglstill or heater.

i `The heat exchange in the reflux tower 21 cools and partly condenses the vapors and preheats the fresh oil supplied directly to the reservoir 18. Additional refluxing of the vapors may be effected in reflux tower 21 by passing therethrough an amount of fresh oil in excess of that supplied to the .reservoir 18 and discharging this excess through connection 31. Anamount of fresh oil, of a heavier character,'in excess of that y .passed in heat exchanging relation'with the towers and fresh lighter oil preheated in the vapors vin reflux tower 2 1 lmay be supplied,

directly to the reservoir 18 by means of bypassv connection 30. During periods when fresh oil is not supplied to the reservoir 18, as at the beginning or end of 'a run,'the reflux tower 21 may be cooled by oil circlilated therethrough and discharged through connection 31. Fresh oil, of a lightercharacter, supplied from receptacle 33 by means of pump 35, is passed in indirect heat exchanging relation with the vapors' in reflux tower 22, the vapors being thereby further cooled and condensed and the fresh oil preheated, and the thus preheated fresh `oil is discharged into receptacle 16. By-pass connection 38v is provided between connections 36 and 37 to and from the reflux tower 22 to permit supply from receptacle 33 to receptacle 16 of an amount of the fresh oil in excess of that passed through the reflux tower 22. Vapors from reservoir 18 escaping through connection 20 pass first through the reflux tower 21 and then through 'the reflux tower 22 from which vapors remaining uncondensed escape `through connection 23 to a condenser (not shown) in which the vapors of the cracked oil, forming the desired cracked distillate, are condensed. Reflux condensate from both tower 21 and tower 22 collects in rev ceptacle 16. This reflux receptacle 16 may be insulated, and the reflux condensate, together with admixe'd fresh oil may be supplied therefrom to the heating tubes at aV more or less elevated temperature.

The oil mixture collecting in receptacle 16, includingreflux condensate from the refluxing operations carried out in both reflux v second refiuxing operation, is supplied to the pump 3 through connection 17 and forced thereby through the heating tubes 2. Additional fresh oil, of a lighter character, may be supplied to the heating tubes in admixture with the oil from receptacle 16 by means of pump 3 from tank 14 through connection 15, or a separate pump may be used for supplying such additional fresh lighter oil the reservoir 18 through'pipe 19 supply heat v thereto and also assist in maintaining uniform conditions throughout that body by the agitation provided. Additional heat may be supplied to the reservoir 18 by means of furnace 32, for example to balance radiation losses, or, and more advantageously, this reservoir may be externally unheated and the body of oil thereiuheated internally only by the hot products discharged from the single pass heater. The reservoir 18, particularly where it is heated internally only, and the connections. between the single pass heater and the reservoir, may with advantage be insulated to prevent heat loss. A connection 26 lis shown for withdrawing tar and fluid residues from the reservoir 18. The unvaporized residue of the oil disy charged into this reservoir from the single pass heater and the unvaporized residue of the fresh heavier oil independently introduced into the reservoir may be discharged through this connection.` Pressure in the system may be'maintained and regulated by valve 24 arranged between the reservoir 18 and the reflux towers 21 and 22, 'or by valve A The pressure in the As an example of one particularly advantageous method of operation ofthe apparatus illustrated in the drawings, in the coinbined treatment of a heavy gas oil, a light` gas oil and a kerosene character distillate, according to the invention, l`the lightest or 'kerosene character` distillate may be supplied from the receptacle 14 directly to the single-pass heating conduit 2 where it is heated to a temperature of from about 800 to 12000 F. Thehea'vy gas oil may be supplied from the receptacle 27 lby the pump 34 to the heat exchanger or reflux tower 21and from thence to the reservoir 18 through connection 28 and pipe 29. lThe light gas oil may be supplied from the receptacle 33-by pump 35 to the reflux tower 22. The body of oil in the reservoir 18 may advantageous- 1y be maintained ata temperature of 700 to 850 F. The vapors liberated in the rcservoir 18 pass successively throughthe reflux towers'21 and22.`The vapors in the reflux tower 22 are subjected to a refluxing operatinby indirect heat exchange vwith the light gas oil supplied thereto from receptacle '33 and the light gas oil preheated thereby. vThe head temperature of the ias fresh oil supplied thereto, to produce a distillate having the desired end point. All of the lightest or kerosene character distillate may thus be required to pass through the single pass heating conduit where it isby indirect heat exchange with the vaporsV in the second refluxing operati/on, that carried out in refiux tower 22 in the apparatus illustrated, and the vapors thereby cooled and refluxed, without any possibility of entrainment of such fresh oil in the vapors escaping from the refluxing operation. A rerun pressure distillate bottoms, remaining after separation of gasoline from a pressure distillate by redistillation, for example, may be handled advantageously in carrying out the present invention by passing it in `indirect heat exchanging relation with the vapors in the second refluxing operation and then forcing it, in admixture with reflux condensate, through the single pass heater into the body of oil in the reservoir. In carrying out the present invention, it will be noted that while the preheated fresh oil from the second refluxing operation may be admixed with reflux condensate therefrom the mixture does not take place Within the refiuxing operation itself.

It is apparent that various modifications of the process embodying the invention may be made, for example, in the combinedtreatment of two grades of oil, the heavier oil may be supplied. from Vthe' container 27 to the reservoir 18 while the'lighter oil may be supplied entirely through the 'reflux tower .22 from the receptacle 33 or part of the lighter oil may de directly introduced into the heating conduit 2 from the receptacle 14 or supplied from receptacle 33 through connection 38. When possible, however, it is advantageous to regulate the refuxing operation as desired by the introduction of a portion of the lighter oil to the reflux tower 2 2 and to introduce any excess of the lighter o il, above that required to produce the desired refiuxlng action, directly into the heatA ing conduit.

I claim: j l. An improved process for cracking hydrocarbon oils comprising passing a 'stream of oil once through a heating conduit and heating it toa cracking temperature therein, discharging the hot products yfrom the heating conduit directly into a body of oil maintained in a reservoir at a cracking temperature, taking off vapors .from the reservoir and subjecting them successively to a first and a second refllixing operation, passing fresh relatively refractory oil in indirect vapors in the second refluxing operation thereby cooling and refluxing the vapors and preheating this fresh oil, and -forcing reflux condensate. from both refluxing operations together with fresh oil preheated in the second refluxing operation through said heating conduit. Y

2. An improved process for cracking hy-I.

drocarbon oils comprising passing a stream of oil once through a heating conduit and heating it to a cracking temperature therein,.

discharging the hot products from the heating conduit directly into a body of oil malntained in a reservoir at a cracking temperature, taking off vapors from the reservoir and subjecting them successively to a first and a second refluxing operation, passing fresh relatively refractory oil in indirect heat exchanging relation with the vapors 1n the first-refluxing operation and thereby cooling and refluxing the vaporsand pre-l heating the fresh oil, supplying fresh oil so preheated to the body of oil in the reservoir, Y

passing fresh relatively more refractory oil in indirect heat exchanging relation with the vapors in` the second refluxing operation thereby cooling and refiuxing the vapors and preheating this fresh oil, and forcing reflux condensate from both refluxing operations together with fresh oil preheated in the second refluxing operation through said heating conduit, the body of oil in the reservoir being externally unheated but heated internally by .the hot products discharged into it from said heating conduit.

3. An improved process for cracking hydrocarbon oils comprising passing a stream of oil once through a heating conduit and heating it to a cracking temperature therein, discharging the hot products from the heating conduit directly into a body of oil maintained in a reservoir at a cracking temperature, taking off vapors from the reservoir and 'subjecting them successively to a first and a vsecond refluxing fresh relatively refractory oil in indirect heat exchanging relation'with the vapors in the first refluxing operationiand thereby cooling and refluxing the vapors and preheating the fresh oil, supplying fresh oil so preheated to the body of oil in the reservoir,

passing relatively morevrefractory oil operation, passing in indirect heat exchanging relation with 'the ing conduit, the stream of oil passed throughcondensate from both reuxing operations the heating conduit being heated therein to a thereby cooling and reluxing the vapors and cracking temperature higher than that main- 10 preheating this fresh oil, and forcing reflux tained in the body of oil n the reservoir. 5 condensate from both refluxing operations In Witness whereof, I have subscribed my together with fresh oil preheated in the secname. Y, I

ond refiuxing operation through said heat- EDWARD W. ISOM.y

Creamware or comemos.

4Patent No. 1,722,147. Y cram-ld my z3, ma, w

EDWARD wl isola,

It is hereby certified that error appears in the printedepecification ofthe above numbered patent requiring correction as ioliows: Page-a, hoef?, for the word "lighted" read "iighter page 5, line 2,]vci`aim 3, etrihe out the .words -"condensa'te"` from both rehming operations" and insert instead "vapors m the second refluxing operatior; and' that the seid Letters 'Patent sbouid be read with this correction therein that the same mayv cmform tothe record of the case in the Patent Office. A

Signed and sealed this 10th day ci September, A.. D. w29.V

Mc J.V Moore, i v (Seal) Actim Gommiwioalenoi Patents. 

